By Jackie Fortiér | KFF Health News

You’re pregnant, healthy, and hearing mixed messages: Health and Human Services Secretary Robert F. Kennedy Jr., who is not a scientist or doctor, says you don’t need the covid vaccine, but experts at the Centers for Disease Control and Protection still put you in a high-risk group of people who ought to receive boosters. The science is on the side of the shots.

Pregnant women who contracted Covid-19 were more likely to become severely ill and to be hospitalized than non-pregnant women of the same age and demographics, especially early in the covid pandemic.

A meta-analysis of 435 studies found that pregnant and recently pregnant women who were infected with the virus that causes covid were more likely to end up in intensive care units, be on invasive ventilation, and die than women who weren’t pregnant but had a similar health profile. This was before covid vaccines were available.

Neil Silverman, a professor of clinical obstetrics and gynecology and the director of the Infectious Diseases in Pregnancy Program at the David Geffen School of Medicine at UCLA, said he still sees more bad outcomes in pregnant patients who have covid.

The risk of severe covid fluctuated as new variants arose and vaccinations became available, Silverman said, but the threat is still meaningful. “No matter what the politics say, the science is the science, and we know that, objectively, pregnant patients are at substantially increased risk of having complications,” Silverman said.

A request for comment regarding the scientific literature that supports covid vaccination for pregnant women sent to HHS’ public affairs office elicited an unsigned email unrelated to the question. The office did not respond when asked for an on-the-record comment.

Kennedy, a longtime anti-vaccine activist before joining the Trump administration, announced May 27 that covid vaccines would be removed from the CDC’s immunization schedule for healthy pregnant women and healthy children. His announcement, made in a video posted on the social media platform X, blindsided CDC officials and circumvented the agency’s established, scientific processes for adding and removing shots from its recommended schedules, The Washington Post reported.

There’s still much unknown about how covid affects a pregnant person. The physiological relationship between covid infections and mothers and fetuses at different stages of a pregnancy is complex, said Angela Rasmussen, a virologist at the University of Saskatchewan.

The increased risk to pregnant patients comes in part because pregnancy changes the immune system, Rasmussen said.

“There is natural immune suppression so that the mother’s body doesn’t attack the developing fetus,” Rasmussen said. “While the mother does still have a functioning immune system, it’s not functioning at full capacity.”

Pregnant patients are more likely to get sick and have a harder time fighting off any infection as a result.

In addition to changing how the immune system works, being pregnant also makes women five times as likely to have blood clots. That risk is increased if they contract covid, said Sallie Permar, chair of pediatrics at Weill Cornell Medicine.

The virus that causes covid can affect the vascular endothelium — specialized cells that line blood vessels and help with blood flow, Rasmussen said. In a healthy person, the endothelium helps prevent blood clots by producing chemicals that tweak the vascular system to keep it running. In a person infected with the covid virus, the balance is thrown off and the production of those molecules is disrupted, which research shows can lead to blood clots or other blood disorders.

Permar said that those clots can be especially dangerous to both pregnant women and fetuses. Inflammation and blood clots in the placenta could be connected to an increased risk of stillbirth, especially from certain covid variants, according to studies published in major medical journals as well as by the CDC.

When the placenta is inflamed, it’s harder for blood carrying oxygen and nutrients to get to the developing baby, said Mary Prahl, an associate professor of pediatrics at the University of California-San Francisco School of Medicine.

“If anything is interrupting those functions — inflammation or clotting or differences in how the blood is flowing — that’s really going to affect how the placenta is working and being able to allow the fetus to grow and develop appropriately,” she said.

It makes sense that we see the effects of covid in the placenta, Silverman said. “The placenta is nothing more than a hyper-specialized collection of blood vessels, so it is like a magnetic target for the virus.”

Blood vessels in the placenta are smaller and may clot more easily than in the mother’s circulatory system, he said.

Permar said recent data suggests that pregnant women sick with covid still have a higher risk of pregnancy complications such as preeclampsia, preterm birth, and miscarriage, even with existing immunity from previous infection or vaccination. Covid, she said, can still land women in the hospital with pregnancy complications.

Prahl said the connection between stillbirth and covid may be changing given the immunity many people have developed from vaccination or prior infection. It’s an area in which she’d like to see more research.

There’s already strong evidence that both mRNA-based and non-mRNA covid vaccines are safe for pregnant women.

Prahl co-authored a small, early study that found no adverse outcomes and showed antibody protection persisted for both the mother and the baby after birth. “What we learned very quickly is that pregnant individuals want answers and many of them want to be involved in research,” she said. Later studies, including one published in the journal Nature Medicine showing that getting a booster in pregnancy cut newborn hospitalizations in the first four months of life, backed up her team’s findings.

Prahl expects more evidence will be available soon to support the benefits of mothers receiving a covid booster during pregnancy.

“I can say, kind of behind the scenes, I’m seeing a lot of this preliminary data,” she said.

She blames the delay in part on the Biden administration’s scaling back of federal efforts to track covid. “A lot of the surveillance of these data were pulled back,” she said. The Trump administration is further cutting money used to track covid.

But because the vaccines give a pregnant woman’s immune system a boost by increasing neutralizing antibodies, virologist Rasmussen is confident that getting one while pregnant makes it less likely a pregnant woman will end up in the hospital if she gets covid.

“It will protect the pregnant person from more severe disease,” she said.

Getting a covid vaccine while pregnant also helps protect newborns after birth. Pregnant women who get vaccinated pass that protection to their young babies, who can’t get their own shots until they are at least 6 months old.

According to data released by the CDC in 2024, nearly 90% of babies who had to be hospitalized with covid had mothers who didn’t get the vaccine while they were pregnant.

As recently as April 2024, research showed that babies too young to be vaccinated had the highest covid hospitalization rate of any age group except people 75 and older.

The Trump administration’s decision to remove the covid vaccine from the list of shots it recommends for pregnant women means insurance companies might no longer cover it. Pregnant women who want to get it anyway may have to pay hundreds of dollars out-of-pocket.

“I don’t want to be that doctor who just says, ‘Well, it’s really important. You have to vaccinate yourself and your kids no matter what, even if you have to pay for it out-of-pocket,’ because everyone has their own priorities and budgetary concerns, especially in the current economic climate,” Silverman said. “I can’t tell a family that the vaccine is more important than feeding their kids.”

But he and his colleagues will keep advising pregnant women to try to get the shots anyway.

“Newborns will be completely naive to covid exposure,” he said. “Vaccinating pregnant women to protect their newborns is still a valid reason to continue this effort.”

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